Valve lifter



Aug 3, 1965 G. H. RoBlNsoN ETAL 3,198,182

VALVE LIFTER Filed Aug 17, 1962 i, 52 i 50 V/l/l//Il/ ATTORNEY UnitedStates Patent O 3,198,182 VALVE LIFTER George H. Robinson, Rochester,and Edward R. Mantel,

Warren, Mich., assignors to General Motors Corporation, Detroit, Mich.,a corporation ot Delaware Filed Aug. 17, 1962, Ser. No. 217,700 Claims.(El. 12S-$0) This is a continuation-in-part of the now abandoned UnitedStates application Serial No. 114,697, filed June 5, 1961, and assignedto the assignee of the present invention.

This invention relates to valve lifters for transmitting movement from acam or the like to the stem of a poppet valve such as is used ininternal combustion engines and more particularly to an improved valvelifter and a method for manufacturing the valve lifter.

The general design of valve lifters in common use today comprises agenerally cup-shaped cylinder which is slidably reciprocable in a boreprovided therefor in the engine crank case so as to Contact the enginedriven cam and a separately formed member which is thrustably supportedin the lifter cylinder and serves to transmit movement from the lifterto the push rod, lt is particularly important in valve lifterconstruction that the valve lifter working surface or foot as it iscalled in the art, operating against the cam, be formed of awearresistant material since these contacting parts are subject tosevere wear conditions in service. It is the object of this invention toprovide an improved valve lifter and a method for its manufacture. It isa more specific object of this invention to provide a valve lifterhaving a more wear-resistant foot portion.

These and other objects are accomplished by preparing an intimatemixture of powdered carbon, tungsten, molybdenum, silicon and iron incertain proportions nad compressing them to form a thin briquette orwafer in a manner well known in powdered metallurgy art. The valvelifter working end is preferably provided with a peripheral retainingridge or lip whereby a shallow cavity is formed within the ridge. Thebriquette is then placed within the cavity and the briquette andadjacent valve lifter surface are subjected to heat at a temperature inthe vicinity of 2200 F. for a time sumcient to cause the constituents ofthe briquette to fuse together and effect a diiiusion bond with thesteel face. On completion of the fusion cycle the interior of the steelbody is cooled rapidly to promote directional solidication of thecoating alloy from the valve lifter surface alloy interface outward,thus preventing formation of internal shrinkage cavities in the coating.

Other objects and advantages of the invention will be apparent from thefollowing detailed description made in relation to the accompanyingdrawing, in which:

FlGURE 1 is a fragmentary elevation View of a valve tappet in its engineenvironment;

- FIGURE 2 is a cross-sectional View of a valve tappet body; and

FlGURES 3, 4 and 5 are fragmentary cross-sectional views illustratingsequential steps in the process of this invention.

As shown in FIGURE 1 of the drawings, a valve lifter consists of acylindrical-shaped body closed at one end 12 and open at the oppositeend 13, which is slidably re- 3,103,182 Patented Aug. 3, 1965 iceciprocable in a bore 1d of an internal combustion engine crank case 16.Within the open end 13 there is received the lower end of a push rod 18and a push rod seat meniber 20 seated on an annular shoulder 21 of thebody 10 by which thrust is transmitted between the lifter body 10 andthe push rod during engine operation. Overlying the seat member 20 andthe shoulder 21 there is provided a thin metal retaining washer 23. Thewasher is relatively exible and of somewhat greater diameter than theopening 15 so that on being radially deflected and forced against thisopening, as shown, it will contract su'lciently to enable it to enterthe opening. It may readily be seen that an upward movement of the rod18 causes the washer to lock or wedge against the opening 15 and to lockthe seat 20 within the valve lifter.

This invention is concerned with a method of making a lifter body 10 andin particular a method of providing the closed end 12 with an end face2d or foot of a wearresistant material. In general the method involvesfirst forming a cup-like member consisting of a cylinder which is closedon one end sach as is shown in FIGURE 2 by a simple upsetting or coldextrusion operation. The dies employed in this operation also providethe closed end of the valve lifter with the' peripheral ridge 26 ofabout 0.015 inch in height which terminates in a relatively narrow edge28 and has an inwardly slanting side 30. This side 30 may suitably slantat an angle of about 45. The height of the ridge 26 may suitably varyfrom about 0.010 inch to about 0.030 inch. As will be hereinafterexplained in detail, the process of this invention involves theapplication of a wear-resistant alloy within the cavity defined by theridge 26.

After the upsetting operation the surfaces of the lifter between theridge 2o are preferably grit blasted to clean them. A powdered metalmixture is next prepared which preferably consists of, by weight, 2.6%carbon, 4% molybdenum, 4% tungsten, 2.0% silicon and the balance iron.These materials are present in the form of powders preferably having aparticle size which will pass a mesh screen. The powders are thoroughlymixed and then compressed under a pressure of about 30 tons per squareinch into a briquette 32, FIGURE 3, preferably having a thickness ofabout 0.15 inch.

Suitable valve lifter working surfaces may be made in accordance withthis invention by providing a briquette in which the carbon is presentbetween about 2.0% and 3.5 by weight, the molybdenum at least 2.0% byweight, and the tungsten at least 2.0% by weight, the sum of the`molybdenum and tungsten being not greater than about 12.0% by weight,and the silicon about 1.0% to 3.5% by weight and the balancesubstantially iron. Preferably the retaining lipy 26 is formed about0.02 inch in height and the briquette is maintained within a thicknessrange of 0.1 inch to 0.2 inch.

After the briquette has been formed, it is preferably sintered to obtainincreased strength for handling efficiency and then placed within thecontines of the cavity of the retaining lip 26. The briquette ispreferably suiciently smaller in diameter than the valve lifter so thatit rests liatly on the lifter surface within the ridge 26 as shown inFIGURE 4. Preferably a linx such as boraX is next sprinkled over thebriquette. The briquette and adjacent valve lifter surface are thensubjected to heat within a temperature range of about 2200 F. to 2400"F. by means of an induction coil 22 as shown in FIGURE face and thebriquette. Heatingtemperatures in excess of 2400 F. may be used.However, no advantage is obtained at higher temperatures. Higher'heating'temperatures tend to cause excessive erosion of the retainingridge 26 and for this reason are undesirable. The heating operationcauses the powdered metal to fuse to form a coating alloy 24` In thisheating operation the flux pro- Y the fused coating has a compositionofabout. 2.1% 'carv bon,1.5% Vsilicon,.4.0% tungsten, 4.0% molybdenum,and .the balance iron. It will be noted that the composition kof thefused coating involves a loss of about 0.5 by Weight each of carbon andsilicon. During the fusion composition. This reduces the melting pointof the iron to a temperature inthe Vicinity of 2200 F. At thistemperature, the tungsten and molybdenum dissolve into the moltenferrous metal. The molten alloy flowsacross the valve lifter surface soas to form a relativelysmooth coating extending betweenfthe extremitiesof the ridge 26. During the heating step, the alloy, and particularlythe 4carbon thereof, diffuses into the steel body to form a strongdiffusion bond. It Will, of course, be understood that it is thediffusion coating ranges which are essential to the high qualityperformance of the valve lifter of this 1 invention.` `The briquettecomposition may be varied to take intor account process variables whichmay result in a greater orlesser loss of carbon and silicon.

On completion of the fusion cyclefthe interior of the steel body iscooled rapidly, preferably by means of a,

small water jet 34 inserted Withinthe valve lifter body as shown inFIGURE 5 to promote directional solidilication ofthe coating alloy fromthe alloy-steel interface outward, thus preventing formation of internalshrinkage cavities in the coating. Preferably the heating operation isconducted in a protective atmosphere of nitrogen or suitable endothermicgenerated gas to prevent excessive oxidation of the metals duringheating. After cooling, the coating is ground to a thickness Preferablyin the range of about 0.01 inch to 0.03 inch and other portions of thevalve lifter are ground to size. Finally, the entire valve lifter iscarburized to provide the side Walls thereof with a Wear-resistantsurface. This involves heating the lifter in a suitable carburizationatmosphere to a temperature in the range of about 155051?. to 1650 F. Asa consequence of this heating operation a carbon case is,

ran important advantage of this inventtion.

'The method of this invention has a numbef of important advantages. Inaddition to its excellent Wear resistance, the use of an iron base alloybriquette or coating cycle, the carbon diffuses into the iron. particleswhich in their original form are of a relatively pure lovv carbon 0.010Vinch to 0.020 inch in. thickness. The method of this invention may beemployed to apply wear-resistant coatings of any thickness andespecially thin coatings with a negligible Waste of coating materials.The presence of the retaining lip 26 is Yessential in that it serves asa dam while the coating alloy is yet molten and thereby insures that thecoating layer will' be of a satisfactory thickness which will extenduniformly over the entire area of the valve lifter Working surface...Although induction heating is preferred because the heating is therebycarefully controlled, satisfactory results have been obtained by heatingwith an-acetylene llame.

In `the preferred embodiment of the invention as described above. thevalve lifter body is formed from an extrudible low carbon steel suchas,l for example, SAE 1018 steel-containing about 0.15% to 0.20% carbon,0.6% to 0.9% manganese, a maximum of 0.04% phosphorus and a maximum ofV0.05% sulfur. In some instances, it may be desired to make the valvelifter of a stainless steel to provide it With resistance to corrosion.VIt has beenfound that typical hardenable stainless ysteels such asthose containing 0.95% to 1.2% carbon and 16% to 18% chromium tend toharden-during the-application of the footvcoatingasdescribed above. Thisresults in a cracking of the coating due to volume increase ortransformation stresses produced in the hardening Aoperation.Howevenstainless steel valve lifters may be provided in accordance withthis invention by using a non-v hardenable stainless steel such as theSAE 430 stainless steel containing about 0.172% carbon maximum and 14%to 18% chromium. The Wear-resistant coating is applied to the foot asdescribed above. The lifter Vis then ground tosize and carburized as inthe case of the low carbon steel.

While this Vinventionhas been described with vreference toV certainpreferred embdiments and Conditions, it Vwill be understood'that theinvention is not limited thereby and that changes and modifications willbe apparent to those Vskilled in theV art VWithoutdeparting from thespirit and principles `of the invention.

We claim: 1

1.Y A valve liftercomprising a metal tubular body closed on one endthereofto form a base,`said base having a fused coating thereoncomprising by Weight 1.5% to 3.0%

carbon, at least 2% molybdenum and at least Y2% tungsten, the sum ofthel molybdenum and tungsten being not greater'than 10%, silicon 0.5 to3.0% and the balance substantially iron. f f

2. A valve lifter LcomprisingV a low vcarbon steel tubular body elementclosed on one Vend thereof to form a base, said base having a fusedcoating thereon comprising by Weight 1.5% to 3.0% carbon, at least 2%molybdenum and at least 2% tungsten, the sum of the molybdenum andtungsten being not greater than 10%,(silicon 0.5 to 3.0% and thebalance'substantiallyiron 3. A valve lifter comprising a ferrous metaltubular body closed at one end thereof to form a base and a wear--resistant ferrous alloycoating on said base comprising promotes theformation of a strong diifusionbond between the coating and theA steelbody. In addition the relatively high carbon content of the alloyresults in carburization of the underlying steel during the fusingvprocess and thus provides a layer 36 of harder steel for supporting`theV coating Vunder high contactloads. The carburized layer 36 in thepreferred embodiment is abouty 0.015 inch. Typically, this ,carburizedlayer is about by Weight 1.5 %to 3.0% carbon, at least 2% molybdenum andat least 2% tungsten, the sum of the molybdenum and tungsten being notgreaterthan 10%, silicon 0.5 to 3.0% and the balance substantially iron,the ferrous metal base underlying said coating having a carburized layerforming a hard support for said coating. l

4. A'valve lifter comprisinganintegrally formed ferrous metal tubularbody closed at one end thereof to form a'base and having a peripheralridge projecting from said base forming .a recess and a Wear-resistantferrous alloy coating on said base within said recess comprising byweight 1.5% Yto 3.0% carbon,'at leastV 2% molybdenum and atleast 2%tungsten,the sum of the molybdenum and tungsten being not greater than10%, silicon 0.5% Yto 3.0% and the balance substantially iron, theferrous metal base underlyingY said coating having a carburized layerforming a hard support for said coating.

5. A machine element having a surface resistant to Wear under highcontact stress and high sliding velocity conditions comprising a ferrousmetal base having a fused coating thereon forming said surfacecomprising by Weight 1.5 to 3.0% carbon, at least 2% molybdenum and atleast 2% tungsten, the sum of the said molybdenum and said tungstenbeing not greater than 10%, silicon 0.5% to 3.0% and the balancesubstantially iron.

References Cite by the Examiner UNITED STATES PATENTS 3/32 Wetherald29-156.7 7/51 Gippert 75-123 2/58 Bolkcom et al. 75-123 6/58 Purchas123-90 8/58 Cobo 123-90 5/61 Carlson 29-156.7

FOREIGN PATENTS 9/58 Great Britain.

FRED E. ENGELTHALER, Primary Examiner.

KARL J. ALBRECHT, RICHARD B. WILKINSON,

Examiners

4. A VALVE LIFTER COMPRISING AN INTEGRALLY FORMED FERROUS METAL TUBULARBODY CLOSED AT ONE END THEREOF TO FORM A BASE AND HAVING A PERIPHERALRIDGE PROJECTING FROM SAID BASE FORMING A RECESS AND A WEAR-RESISTANTFERROUS ALLOY COATING ON SAID BASE WITHIN SAID RECESS COMPRISING BYWEIGHT 1.5% TO 3.0% CARBON, AT LEAST 2% MOLYBDENUM AND AT LEAST 2%TUNGSTEN, THE SUM OF THE MOLYBDENUM AND TUNGSTEN BEING NOT GREATER THAN10%, SILICON 0.5% TO 3.0% AND THE BALANCE SUBSTANTIALLY IRON, THEFERROUS METAL BASE UNDERLYING SAID COARING HAVING A CARBURIZED LAYERFORMING A HARD SUPPORT FOR SAID COATING.